The USL NASA PC R and D interactive presentation development system

The Interactive Presentation Development System (IPFS) is a highly interactive system for creating, editing, and displaying video presentation sequences, e.g., for developing and presenting displays of instructional material similiar to overhead transparency or slide presentations. However, since this system is PC-based, users (instructors) can step through sequences forward or backward, focusing attention to areas of the display with special cursor pointers. Additionally, screen displays may be dynamically modified during the presentation to show assignments or to answer questions, much like a traditional blackboard. This system is now implemented at the University of Southwestern Louisiana for use within the piloting phases of the NASA contract work

A Programming Environment Evaluation Methodology for Object-Oriented Systems

The object-oriented design strategy as both a problem decomposition and system development paradigm has made impressive inroads into the various areas of the computing sciences. Substantial development productivity improvements have been demonstrated in areas ranging from artificial intelligence to user interface design. However, there has been very little progress in the formal characterization of these productivity improvements and in the identification of the underlying cognitive mechanisms. The development and validation of models and metrics of this sort require large amounts of systematically-gathered structural and productivity data. There has, however, been a notable lack of systematically-gathered information on these development environments. A large part of this problem is attributable to the lack of a systematic programming environment evaluation methodology that is appropriate to the evaluation of object-oriented systems

The USL NASA PC R and D development environment standards

The development environment standards which have been established in order to control usage of the IBM PC/XT development systems and to prevent interference between projects being currently developed on the PC's are discussed. The standards address the following areas: scheduling PC resources; login/logout procedures; training; file naming conventions; hard disk organization; diskette care; backup procedures; and copying policies

USL/DBMS NASA/PC R and D project system design standards

A set of system design standards intended to assure the completeness and quality of designs developed for PC research and development projects is established. The standards presented address the areas of problem definition, initial design plan, design specification, and re-evaluation

Three-dimensionality in quasi-two dimensional flows: recirculations and barrel effects

A scenario is put forward for the appearance of three-dimensionality both in quasi-2D rotating flows and quasi-2D magnetohydrodynamic (MHD) flows. We show that 3D recirculating flows and currents originate in wall boundary layers and that, unlike in ordinary hydrodynamic flows, they cannot be ignited by confinement alone. They also induce a second form of three-dimensionality with quadratic variations of velocities and current across the channel. This scenario explains both the common tendency of these flows to two-dimensionality and the mechanisms of the recirculations through a single formal analogy covering a wide class of flow including rotating and MHD flows. These trans-disciplinary effects are thus active in atmospheres, oceans or the cooling blankets of nuclear fusion reactors.Comment: 6 pages, 1 Figur

Indeterminacy, Memory, and Motion in a Simple Granular Packing

We apply two theoretical and two numerical methods to the problem of a disk placed in a groove and subjected to gravity and a torque. Methods assuming rigid particles are indeterminate -- certain combinations of forces cannot be calculated, but only constrained by inequalities. In methods assuming deformable particles, these combinations of forces are determined by the history of the packing. Thus indeterminacy in rigid particles becomes memory in deformable ones. Furthermore, the torque needed to rotate the particle was calculated. Two different paths to motion were identified. In the first, contact forces change slowly, and the indeterminacy decreases continuously to zero, and vanishes precisely at the onset of motion, and the torque needed to rotate the disk is independent of method and packing history. In the second way, this torque depends on method and on the history of the packing, and the forces jump discontinuously at the onset of motion.Comment: 11 pages, 7 figures, submitted to Phys Rev

USL/DBMS NASA/PC R and D project C programming standards

A set of programming standards intended to promote reliability, readability, and portability of C programs written for PC research and development projects is established. These standards must be adhered to except where reasons for deviation are clearly identified and approved by the PC team. Any approved deviation from these standards must also be clearly documented in the pertinent source code

Measurement of Indeterminacy in Packings of Perfectly Rigid Disks

Static packings of perfectly rigid particles are investigated theoretically and numerically. The problem of finding the contact forces in such packings is formulated mathematically. Letting the values of the contact forces define a vector in a high-dimensional space enable us to show that the set of all possible contact forces is convex, facilitating its numerical exploration. It is also found that the boundary of the set is connected with the presence of sliding contacts, suggesting that a stable packing should not have more than 2M-3N sliding contacts in two dimensions, where M is the number of contacts and N is the number of particles. These results were used to analyze packings generated in different ways by either molecular dynamics or contact dynamics simulations. The dimension of the set of possible forces and the number of sliding contacts agrees with the theoretical expectations. The indeterminacy of each component of the contact forces are found, as well as the an estimate for the diameter of the set of possible contact forces. We also show that contacts with high indeterminacy are located on force chains. The question of whether the simulation methods can represent a packing's memory of its formation is addressed.Comment: 12 pages, 13 figures, submitted to Phys Rev

Interaction périphyton-benthos en milieu acidifi

Plusieurs études relevées dans la littérature expliquent l'augmentation de la biomasse du périphyton aux bas pH par la diminution de la prédation par le benthos, les larves herbivores paraissant être les plus sensibles à l'acidification. Cependant cette hypothèse n'a pas reçu de vérification expérimentale directe. La présente étude analyse l'évolution de la biomasse et de la production périphytique en présence et en absence de macrobenthos à deux valeurs de pH, soit 6,3 ± 0,1 et 4,2 ± 0,2. Pour ce faire nous avons travaillé en conditions semi-naturelles, dans des canaux artificiels alimentés par un ruisseau. Des plaques de céramique non vernie étaient introduites dans des cylindres de plexiglas transparent. Après le début de l'acidification, la moitié des cylindres étaient fermés avec du filet de Nytex à maille de 160 µm. Bien que ce dispositif d'exclusion ne se soit pas avéré totalement efficace, des différences notables sont observables entre cylindres ouverts et fermés en condition acidifiée. Après un mois d'acidification, il y a dans les cylindres fermés une accumulation de biomasse, une réduction de la production et un rapport P/B très faible; situation caractéristique d'une réduction de la pression de broutage selon le modèle de Lamberti et Moore. L'évolution de la biomasse et de la production périphytique en condition acidifiée semble donc être dépendante de la réduction du broutage.Many studies attribute the increased biomass of periphyton at low pH to a decrease in grazing by benthic invertebrates. Herbivorus larvae appear to be the most sensitive to acidification. However this hypothesis bas not received direct experimental verification. The present study analyses the evolution of periphytic biomass and production in the presence and absence of macrobenthos at two pH values, 6,3 ± 0,1 and 4,2 ± 0,2. The study was carried out in semi-natural conditions, using artificial troughs fed by a nearby stream. Unglazed ceramic tiles were placed in transparent plexiglass cylinders. Once acidification had begun, half the cylinders were closed with 160 µm mesh nytex screen. Although this exclusion device was not completely effective, notable differences were observed between the open and closed cylinders in the acidified conditions. After a month of acidification the closed cylinders showed an accumulation of biomass, a decrease in production and a very low P/B ratio; these conditions are characteristic of a reduced grazing pressure according to the Lamberti and Moore model. The evolution of periphytic biomass and production in acidified conditions would thus appear to be determined to some extent by reduced grazing